There is a need for polymer compositions that have improved foaming characteristics (high expansion and smooth surface quality) and reduced water absorption for the targeted foam density. The observed water absorption relates directly to the foamed structure and number of closed cells present in the foam. The foaming process is a delicate balance of the cross-linking of the EPDM and expansion (from a foaming agent, such as CELOGEN OT), which depends highly on the melt elasticity of the EPDM, as well as on the viscosity increase during the expansion and cure cycle. The melt elasticity of the polymer is related to its molecular weight and degree of long-chain branching present. Typical sponge EPDM products, such as VISTALON 8800 (Exxon-Mobil) and KELTAN 7341A (Lanxess), are oil-extended products that are high in molecular weight, and are relatively amorphous. When formulated and vulcanized into a foamed article, these EPDM resins are generally considered the ‘best-in-class’ in terms of water absorption, and foamed properties, such as compression set and tensile. Rubber compositions for foams and/or other applications are also disclosed in the following: US20110233448A1, US6384290B1, US5691413B1, US20090209672, U.S. Pat. No. 4,722,971A, U.S. Pat. No. 5,610,254, US20110160323, WO2009/072503 (abstract), JP2006307100A (abstract), JP2007191497A (abstract), and JP2006335847A (abstract).
However, there is a need for new polymer compositions that have improved foaming characteristics (high expansion and smooth surface quality) and reduced water absorption for the targeted foam density. These needs have been met by the following invention.